Currently, image display methods which enable the presentation of multiple images from different viewing angles fall into three broad categories: projection-type (non-holographic) displays, lens-sheet displays and holographic displays. Any of these methods can be used to display autostereoscopic depth images, motion images and color changing images.
The most common technique of producing projection-type displays is the barrier strip method. A barrier strip display device consists of an interleaved image which typically consists of strips taken from each of the images that are to be displayed. The strips comprising each of the images are interleaved parallel to each other so that every Nth strip is from the same image, where N is the number of images. This number may be as small as two or as large as nineteen or more. The interleaved image is disposed in close proximity to and parallel to a viewing mask. The viewing mask contains parallel opaque lines of equal width which are separated by transparent zones having a uniform width which is equal to or less than that of the opaque lines. Barrier strip images are usually viewed from the mask side by means of light transmitted through the interleaved image and the mask. The intensity of the back illumination required depends on the brightness of the viewing environment and on the number of images which are interleaved. The color that is perceived at a particular point and at a particular viewing angle with a barrier strip display device is determined by the color of the image strip which is visible through the mask at that point.
Though barrier strips are capable of displaying autostereoscopic images, a barrier strip display device will produce this effect only when certain conditions are satisfied. First, the mask lines must lie in a plane orthogonal to that of the observer's eyes. Also, the width and spacing of the transparent mask lines and the distance from the interleaved image to the mask must be such that each of the viewer's eyes sees different, non-overlapping regions of the interleaved image through the transparent mask lines. The interleaved image must have been constructed such that each of the image lines visible to the right eye is part of a right eye stereo pair image, and the image lines visible to the left eye are each part of a matching left eye stereo pair image. The distances and positions at which stereoscopic depth is perceived is restricted by the geometry of the mask, the number of interleaved images and the mask-to-image distance.
In addition to the difficulty in achieving an autostereoscopic effect, a significant limitation on barrier strip image devices is that the thickness of such a device is governed by the number of images it presents, the width of the image strips and the intended viewing distance. The distance between the barrier strips mask and the interleaved image is generally a large multiple of the width of a single image strip. A typical barrier strip device has a thickness of about six (6) millimeters, making it an unacceptable technology for mass production. The barrier strip method is further limited in that it is only useful as a back-illuminated image display method.
Among the most common lens-sheet display techniques are integral photography, integrams and lenticular sheets. Integral photography (referred to in the trade as the "fly-eye" approach) involves photographing an image through a plastic sheet into which small fly's-eye lenses (typically 50,000 lenses per sheet) have been impressed. The lenses cause a complete reproduction of the photographed image to be reproduced behind each tiny lens. This approach can recreate a visually complete three-dimensional image, but can only be reproduced at great expense. A further limitation of this lens sheet is that the images are at such a fine resolution that they cannot be reproduced on printing presses, but have to be reproduced photographically. Images produced by this method also have a very restricted viewing angle within which the image reconstructs correctly.
The integram approach to lens-sheet displays is a complex extension of the fly-eye approach. It involves positioning the captured image along a precisely curved surface (dimensionally matching the focal surface of the fly-eye lens) to overcome the viewing angle restrictions. The expense and difficulty in producing high quality three-dimensional images with this method, however, have prevented any large scale commercial success.
A third method of the lens-sheet display technique currently known is the lenticular screen display device. A lenticular screen display device employs an array of cylindrical lenses to control the viewing angle of interleaved image strip. The lenses are disposed parallel to the image strips between the observer and the image strips such that the image strips directly underneath a lens lies at or near the lens' focal plane. The range of angles through which the image will be visible is determined by the position of each image strip underneath the lens array. As with the barrier strip method, the color of the image strip determines the color that will be perceived at that point of the lenticular screen processed image.
As with the barrier strip method, a significant limitation on the lenticular screen display device is that its thickness is dependent on the width of the image strips. The thickness also is limited by the number of images presented, the designed viewing distance, and the focal properties of the lens. The thickness of these devices is in general greater than the width of the image strip multiplied by the number of images. As a result, a typical lenticular screen display device has a thickness of about one (1) millimeter, making it relatively expensive for mass production, and generally too thick for automated printing press equipment.
The third broad category of currently known methods of producing and displaying autostereoscopic images is holographic displays. Holographic displays use holograms to reconstruct the appearance of an object over an angular range of view without the use of a lens. A hologram is a record of a diffraction pattern representing an object as viewed from a certain range of positions. There are many types of holograms, each of which possesses its own range of viewing conditions. Some holograms require laser illumination for the reconstruction of an image, while others can be viewed by means of incoherent white light. Holograms displaying full color over a range of viewing angles normally require illumination by three lasers--red, blue and green--simultaneously. White light viewable holograms are generally either monochromatic or display a rainbow coloration which varies according to the viewing angle. Holograms are capable of displaying autostereoscopic, motion, combined autostereoscopic and motion, and color-change images. However, creating and reproducing a high quality hologram is a time-consuming and difficult process. Holograms cannot be created by printing and are not easily combined with the mass production of printed articles. Holograms are expensive and difficult to originate. They also require special equipment to impress onto a printing substrate. Because, of their restrictive viewing conditions and limited control of color, the practical applications of holographic displays is very limited.
The present invention provides a device for displaying autostereoscopic and dynamic images which eliminates the need for lenses, as required in conventional lens-sheet display devices, as well as the need for barrier strips, as required inconventional barrier strip display devices. The device of the present invention utilizes an inner optic which illuminates image strips formed in a layer of emulsion. The inner optic also provides the light direction control needed to produce the perception of autostereoscopic depth, motion, or color change.